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Let’s Talk About Sleep

Oh no. It’s 4am, and I’ve done it again. Ugh. I’ve waited until the last minute to write my NeuWriteSD post, and now it’s 4am. And I haven’t slept since 5am yesterday morning. Ugh.

Oprah is sooo over my procrastination.

As you might imagine, I’m feeling pretty terrible. Not only because of the guilt (since I was supposed to have this written two weeks ago), but because I just really want to sleep.

This is me in a few hours. I just want to go to sleep!!!

If this procrastination-followed-by-no-sleep-followed-by-tears-in-cereal thing wasn’t my blogging MO, I would call it ironic… because today’s topic is, of course, sleep.

What is sleep?

It seems like a simple question, but the definition of sleep is actually fairly complex. In a fun review, “Do all animals sleep?” 1, sleep expert Dr. Jerome M. Siegel defines (human) sleep as “a rapidly reversible state of immobility and greatly reduced sensory responsiveness… that is homeostatically regulated.” Homeostatic regulation means that a lack of sleep produces an increased drive for sleep, as well as sleep rebound. Importantly, Siegel also defines sleep as NOT simply circadian changes alertness and activity. That means that any ol’ reduction in responsiveness and activity (i.e., hibernation or torpor) doesn’t necessarily mean sleep.

Beautiful REM and NREM sleep from midnight to 6:30am. Sleep is deepest early on in the night and the duration of REM sleep increases as morning approaches. Note: NREM stages 3 and 4 have recently been collapsed into a single stage. I am sorry for the outdated image from Wikipedia.

There are two main types of sleep:

Rapid eye movement (REM) sleep is characterized by rapid eye movement. This is when our best dreams occur. Brain activity during REM sleep looks similar to that during waking in most brain regions, including the brainstem. Noradrenergic, serotonergic, and histaminergic neurons, which are tonically active during the awake state, however, are silent during REM sleep. The lack of neurotransmitter release during REM sleep leads to reduced muscle tone and paralysis. Another version of REM sleep can be observed in the video below.

Non-REM (NREM) sleep is characterized by a lack of rapid eye movement. And also other important things, such as reduced activity in the brain stem, reduced activity and metabolism in the forebrain, reduced acetylcholine release, and very distinct patterns of brain activity (you know, like sleep spindles and K-complexes and stuff…).

With the above criterion in mind, Siegel ran through the gamut of animals (including single-celled organisms, albeit briefly, as well as insects, birds, reptiles, and marine mammals) and concluded that, no, not all animals sleep… at least not by human standards.

These animals don’t sleep like humans do. A. Commerson’s dolphins are continuously active from birth to death. Amazingly, they are always moving with accurate sensory and motor performance.2B. Bottlenose dolphins never have bilateral slow-wave sleep. That means that when the sleep, only one hemisphere of their brain appears to be “asleep” (this also happens in fur seals). Strangely, there is no asymmetry in their swimming (meanwhile, fur seals have only one eye open and one flipper is inactive).1,3C. Have you seen Blackfish? D. Killer whale babies and their mothers are continuously active 4-6 weeks after birth.2E. Bullfrogs are more responsive to sensory stimuli during their inactive period versus their active period. Also, they do not exhibit REM sleep.4F. Even in captivity, whilte-crowned sparrows have reduced sleep (defined by EEG and behavior) during migrating season. This decrease in sleep does not impair performance in motor tasks and is not followed by sleep rebound.5 Image from Siegel, 2008; caption by yours truly.

In addition to the examples above, zebrafish do not show sleep rebound after their sleep-like state is blocked by light exposure.6 And no one has yet claimed that sleep exists in single-celled organisms or insects.

Thankfully, scientists’ trusty rodents sleep, for the most part, like humans do (with the caveats that they are nocturnal, have different neuroanatomy, and exhibit different patterns of arousal threshold during sleep).

Why do we sleep?

If sleep as we know it is not necessary for all animals, then why do we do it? The exact role of sleep remains elusive, but energy conservation and restoration seem to be the most popular answers. These processes, Siegel notes, can be accomplished by other species in the waking state, so they don’t need sleep like we do.1 Makes sense.

As a neuroscientist, however, it’s my duty to tell you that sleep is also very important for memory consolidation. Consolidation of implicit sensory and motor memories, as well as explicit declarative memories, can benefit from a full night’s sleep or even just a short (~6-minute) nap.7,8

Recently, Yang et al. (2014) looked at the specific neuronal changes that accompany memory consolidation during sleep. The group used in vivo fluoresence and two-photon calcium imaging in mice learning a motor task and found that: 1. dendritic spine formation is correlated with task improvement, 2. the acquisition of different tasks results in changes different, specific sets of dendritic branches, 3. sleep deprivation decreases the number of new spines, 4. sleep makes newly formed spines more likely to persist over time, and 5. neurons activated during newly learned tasks are reactivated during NREM (slow-wave) sleep. 9,10

Yang et al. (2014) demonstrated how slow-wave oscillations, reactivation of recent experiences, and changes in synaptic connectivity are related and contribute to memory consolidation. This is very exciting science and a very cute illustration. Image from Euston & Steenland (2014).

But rather than tell you the benefits of sleep, here’s Wikipedia’s list of bad things associated with the lack of sleep:

Will I die from sleep deprivation?

Sleep deprivation can lead to so many problems and feels so awful right now that I can understand why death-by-sleep-deprivation doesn’t sound that unlikely. In fact, pioneering sleep researcher Dr. Allan Rechtschaffen and colleagues found that 70-90% sleep deprivation of rats led to death within 2 to 3 weeks. Prior to death, these rats lost weight (in spite of increased food intake) and developed fur discoloration and skin lesions. Gross! /Sad. They also exhibited greatly increased body temperature that fell just before death.11

Thankfully, these results have not been replicated in any other species (including humans and pigeons).1,12 So, in short, no one is going to die from sleep deprivation… unless they have fatal familial insomnia, which is terrifying but unlikely.

Will I get sick from sleep deprivation?

Maybe yes, maybe no. As mentioned above, rats lose weight and develop weird skin conditions and fluctuations in body temperature after prolonged sleep deprivation. Fortunately, like death-by-sleep-dep, these intermediate changes in health have not been replicated in humans. In fact, humans tend to gain weight and body temperature falls rather than increases due to sleep deprivation.13

If you continue to take care of other aspects of your health while you fail to sleep, you should be fine. But this is not to say that sleep deprivation doesn’t come without changes in the immune system. There are plenty of changes taking place: IgG, IgA, and IgM antibody concentrations and white blood cell count increase, natural killer cells fluctuate in number and activity, and the number of helper T cells decreases.14,15 So far, though, no one really knows what this means. Some scientists even argue that sleep restriction is beneficial.16 So this is probably the least of your worries.

I want everything about this.

Will I develop psychosis from sleep deprivation?

The real worry is your mental health. This is the question that got me interested in the topic of sleep. In addition to the anxiety, irritability, difficulty paying attention and making decisions, and all of the other annoying cognitive deficits that will occur due to sleep dep, there are also the psychotic effects.

I haven’t been sleeping much, and for a while, I was worried that this lack of sleep 1) is due to mental illness and/or 2) will precipitate mental illness. Anyway, I will address the former question in a future post (Part II), but for now, I’ll say that no, my current level of sleep deprivation will not make me psychotic. Probably. At least not permanently.

Although the first human sleep deprivation study happened in the late 1900s,17 these types of studies really took off in the 1960s. During this period, the “fifth day turning point” was discovered. According to several fascinating studies, it is not until 100 to 120 hours that the psychotic symptoms really set in.18 (Strangely, on the fifth day, subjects also seem to get a “second wind” and sleep deprivation seem more tolerable.19 But maybe that’s because they are also kind of insane.) To be clear, however, hallucinations can begin before the fifth day. The sleep deprived might perceive tingling sensations, hear humming noises and ringing in the ears, or feel as if they are wearing a hat that is not actually on their head… But by the fifth day, hallucinations are more prolonged and paranoid, and full dream-like hallucinations may occur. Paranoid schizophrenic behavior can also set in, resulting in suspiciousness, as well as delusions of grandeur, reference, or persecution. Thankfully for normal subjects, psychotic behavior generally dissipates after a single episode of recovery sleep.18 Even a whopping 205 hours of sleep deprivation, “did not change the directions [the subjects’ lives] were going nor modify their lifestyles… sleep deprivation per se is unable to produce psychopathological reactions which extend beyond the period of sleep deprivation.”19

Timeline of a 205-hour sleep deprivation study by Pasnau et al. (1968). Although none of the four (very interesting) participants developed schizophrenia-like delusions or hallucinations (according to the authors), during the last three days of deprivation, “changes of a regressive nature were observed.” The men played with their food and bathroom activities were “infantilized,” and they were in denial of their behavior. During a psychomotor tracking task near the end of the study, one subject thought a hybrid of Humpty Dumpty + a gorilla was going to attack him. The authors did not consider this to be psychotic but merely a “bad dream.” (Debatable?)

So, basically, we’re going to be okay as long as this sleep deprivation thing doesn’t continue for too long. (And P.S. if you’re low on acid, a couple days of sleep deprivation in advance can really enhance your trip on a dose that’s otherwise too low.20)

Are you sleeping enough?

Before I end this post, I want to make sure that you understand that the “sleep deprivation” described above is extreme. It is important to remember that some people really just don’t need that much sleep! We can adapt to reduced sleep—so although we might be drowsy, our neurobehavioral functioning will resist impairment. And if you’re not drowsy, it’s not worth forcing yourself to sleep, because prolonging sleep beyond your norm doesn’t necessarily enhance performance and can even be detrimental to your health.14

My results from the Munich ChronoType Questionnaire. Apparently, I have a pretty average chronotype: “slight early.” I sleep less on free days than on weekdays… probably because I have “the least problems of all chronotypes to synchronise [my] biological clock with social schedules.” Party time!